TEMPORAL AND SPATIAL VARIATION IN TRANSPIRATION OF NORWAY SPRUCE STANDS WITHIN A FORESTED CATCHMENT OF THE FICHTELGEBIRGE, GERMANY

Tree transpiration was observed with sapflow methods in six Norway spr uce (Picea abies) stands located in the Lehstenbach catchment, Fichtel gebirge, Germany, differing in age (40 years up to 140 years), structu re, exposition and soil characteristics. The seasonal pattern in tree canopy transpiration, with the highest transpiration rates in July, wa s very similar among the stands. However, young dense stands had highe r transpiration compared to older less dense stands. Because of forest management practices, stand density decreases with increasing stand a ge and provides the best predictor of canopy water use. Measured xylem sapflux density did not differ significantly among stands, e.g. vary in correlation with stand density. Thus, differences in canopy transpi ration were related to differences in cumulative sapwood area, which d ecreases with age and at lower tree density. While both total sapwood area and individual tree sapwood area decrease in older less dense sta nds, leaf area index of the stands remains high. Thus, transpiration o r physiological activity of the average individual needle must decreas e. Simulations with a three-dimensional stand model suggest that stand structural changes influence light climate and reduce the activity of the average needle in the stands. Nevertheless, age and nutrition mus t be considered with respect to additional direct effects on canopy tr anspiration. ((C) Inra/Elsevier, Paris.).